In the past funding period we confirmed our major hypothesis that progastrin peptides (PG) exert proliferative/anti-apoptotic/co-carcinogenic effects on intestinal/colonic epithelial cell lines, in vitro and in vivo, and increase the risk of colon carcinogenesis in response to azoxymethane (AOM). Additionally, we made the novel discovery that Annexin II (ANXII) functions as a high affinity receptor for PG and is required for mediating growth factor effects of PG on target cells. An important role of [unreadable]-catenin, c-Src, PI3K/Akt, MAPK/ERK and NFkB in mediating growth factor effects of PG on normal and neoplastic intestinal epithelial cells was also identified. Based on these findings, the major hypothesis of our current grant proposal is that ANXII facilitates the activation of one or more of the above indicated kinases/transcription factors in response to PG. Experiments in Aims 1 and 2 will examine this hypothesis. In Aim 1, PG responsive cell lines, altered for ANX-II expression will be used, as an in vitro model of investigation. For the in vivo studies, we will either use transgenic mice over-expressing PG (Fabp-PG), before or after modulation of ANXII expression. We will either use ANX-II knock out mice, or use specific siRNA for down regulating ANXII expression. In preliminary studies co-localization of PG with ANXII in situ, in cells over-expressing autocrine PG or responsive to exogenous PG was observed. Therefore in Aim 2, pathways mediating intracellular translocation of ANXII/PG, in response to binding of PG to extracellular ANXII (and its functional significance) will be examined;fluorescence based detection techniques and biochemical analysis will be used. In Aim 3 the clinical relevance of our findings will be examined in a pilot correlative study with samples obtained from patients, consented at the time of colonoscopy or at the time of surgical resection of colonic tumors, at different stages of colon carcinogenesis. Our initial studies strongly implicate PG peptides in the progression of the colon cancer disease. Therefore, understanding the role of ANX-II and the various signaling molecules in mediating the actions of PG are clinically important goals. Data obtained from the above studies will facilitate the development of more effective strategies for targeting the actions of PG for preventative and treatment purposes.